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Piston question

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Piston question

Unread postAuthor: Mr.Russ » Fri Jan 26, 2007 9:12 pm

would somebody please explain to me how piston guns work, i'm very interested in air cannons and this would be great to know about. I would like to know basically what you need to make a psiton, what it does etc

thanks
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Unread postAuthor: LGM » Fri Jan 26, 2007 9:19 pm

Well, if you are going to make a piston, you should start with a coaxial. Have the barrel come within a few inches of the rear of the gun. The piston can be made out of almost any material, but for larger guns disks of plastic work well. To fire, release the air behind the piston which will draw it back and allow the air to flow out of the barrel. There are much more detailed directions in the how to section of the site
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Unread postAuthor: Mr.Russ » Fri Jan 26, 2007 9:21 pm

ok thanks for that i'll check it out.
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Unread postAuthor: Insomniac » Fri Jan 26, 2007 9:24 pm

1# Look at the wiki

2# Before asking simple questions like these, use the search button and check the wiki. Seeing as this is your first post its ok, but this question has been asked, and answered several times. Use the search engine!

3#Welcome to spudfiles!
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Unread postAuthor: Mr.Russ » Fri Jan 26, 2007 9:30 pm

1# Ill check the wiki out

2# sorry for not using the search button

3# thanks!
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Unread postAuthor: judgment_arms » Sat Jan 27, 2007 12:43 am

Yes, Welcome to the forums!
I’m in a good mood so here’s a friendly tip:
Use hot glue for your first piston, it’s simple and effective, just take a piece of pipe with the ID you need and using a hot glue gun glue the section of pipe to a piece of wood, spray the inside of the pipe with “Pam” or any spray on non-stick cooking spray. Melt enough hot glue sticks to fill the pipe to the desired thickness, usually about 2-3inches, use a pan that you can just throw out afterwards as it’s a pain in the butt to clean out, after the glue’s all melted pore it into the mold (the piece of pipe). Let cool, DO NOT stick it in the freezer or refrigerator the outside will cool too quickly and it will not come out right.
I hope everything I said made sense; I’m falling asleep at the key-board so it may not have…I’m going to bed now…
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Unread postAuthor: Mr.Russ » Sat Jan 27, 2007 4:10 am

thanks for that
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Unread postAuthor: mark.f » Sat Jan 27, 2007 8:34 am

You can use hot glue, but here's what I did for my first piston valve:

* Find a dowel or rod the about the diameter you need to fit in the piston carriage. I used 1-7/8" PVC rod, but you could probably use some sort of wooden dowel or pipe if you felt like it.
* Two, if it's hollow or porous, seal it up. My first failed piston, I used fiberglass putty. You should probably just use fiberglass RESIN or epoxy.
* Bolt the sealing face to the front of the piston. Make sure you use the right type of screw for the material you're using. If it's soft, use something like a wood screw. If it's hard, use a machine screw and tap the hole to mate with it. I used a wood screw on PVC, just so you know.
* Wrap it in duct tape until it fits. May sound "redneckish", but it works. You can also use electrical tape or something like that, but just remember to service the piston, (re-wrap the last layer), every now and then.

Or, if you really want a quality piston, do this:

* Get some machining stock just a little larger than the inside diameter of your piston carriage. Get somebody with a lathe to turn it down so that it will fit.
* Cut a length of the new stock however long you want your piston to be. Then, cut this length into three equal pieces. I would use a chop saw to do this.
* Use a gasket cutter with a pair of calipers to assist and cut two gaskets approximately .01-.03" smaller in diameter than the inside diameter of the carriage. I would use a pretty thick and soft material, like 1/8" neoprene or nitrile around 50A to 70A. Use the calipers to drill a hole perfectly centered on the two gaskets and the pieces of stock 1/4" wide. Cut a sealing face for the piston smaller than the ID of the carriage. Then, lay them all together and stick a length of 1/4"-20 threaded rod through them, and use hex nuts and some washers to tighten down. Tighten until the gaskets expand to seal in the carriage.
* Find a piece of tubing with a fairly small ID, (like 1/32" to 1/16"), and drill a hole through the piston the outside diameter of the tubing. If it's metal or another hard material, just stick it through. If it's plastic, use some wire to support as you push it through. This will be on the OUTSIDE EDGE of the piston, if it's barrel sealing.

Hope this helped. Regardless of which method you use, I advise to lube the piston with some grease, (the kind that DOESN'T eat into rubbers and seals), and add a bumper to absorb the impact of the piston flying backwards.
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